In the art of manufacturing tires, it is desirable to employ rubber vulcanizates that give reduced hysteresis, i.e., less loss of mechanical energy to heat. For example, rubber vulcanizates that show reduced hysteresis are advantageously employed in tire components, such as sidewalls and treads, to yield tires having desirably low rolling resistance. The hysteresis of a rubber vulcanizate is often attributed to the free polymer chain ends within the crosslinked rubber network, as well as the dissociation of filler agglomerates. Functionalized polymers have been employed to reduce hysteresis. The functional group of the functionalized polymer may reduce the number of free polymer chain ends via interaction with filler particles. Also, the functional group may reduce filler agglomeration. Nevertheless, whether a particular functional group imparted to a polymer can reduce hysteresis is often unpredictable.
Functionalized polymers may be prepared by post-polymerization treatment of reactive polymers with certain functionalizing agents. However, whether a reactive polymer can be functionalized by treatment with a particular functionalizing agent can be unpredictable. For example, functionalizing agents that work for one type of polymer do not necessarily work for another type of polymer, and vice versa.
Lanthanide-based catalyst systems may be useful for polymerizing conjugated diene monomers to form polydienes having high cis-1,4-linkage contents. The resulting cis-1,4-polydienes may display pseudo-living characteristics in that, upon completion of the polymerization, some of the polymer chains may possess reactive ends that can react with certain functionalizing agents to yield functionalized polymers. Also, the cis-1,4-polydienes prepared with lanthanide-based catalysts have a linear backbone structure, which is believed to provide better tensile properties, higher abrasion resistance, lower hysteresis loss, and better fatigue resistance than those of analogous polymers prepared with other catalyst systems such as titanium-based, cobalt-based, and nickel-based catalyst systems. The cis-1,4-polydienes prepared with lanthanide-based catalysts are particularly suitable for use in tire components such as sidewalls and treads.
Because functionalized polymers are advantageous, especially in the manufacture of tires, there exists a need to develop a method for producing lanthanide-catalyzed cis-1,4-polydienes that give reduced hysteresis.